1. Field of the Disclosure
The present disclosure relates to a coupling structure between a sensing magnet and a plate of an EPS motor, and more particularly to an anti-separating structure of a sensing magnet for an EPS motor equipped with a structure to apply a mechanical force to a magnet and a plate, thereby stably preventing the magnet from disengaging to an axial and rotational direction.
2. Discussion of the Related Art
Generally, almost every vehicle employs an electric power-assist steering system. Such an electric power-assist steering system generates an assist force based on the steering torque and the steering angle, so as to enhance the steering performance of the vehicle.
That is, a steering system that assists a steering force of a vehicle with a separate power is used to enhance the motion stability of a vehicle.
Conventionally, the auxiliary steering device uses hydraulic pressure, but an Electronic Power Steering (EPS) system adapted to transmit a rotation output of an electric motor to a steering shaft via a speed reduction mechanism has been increasingly employed these days from a viewpoint of a reduction in engine load, a reduction in weight, an enhanced steering stability and a quick restoring force.
The EPS system is such that an Electronic Control Unit (ECU) drives a motor in response to steering conditions detected by a speed sensor, a torque angle sensor and a torque sensor to enhance a steering stability and provide a quick restoring force, whereby a driver can safely steer a vehicle.
The EPS system is also such that a motor assists a torque manipulating a steering wheel to allow a driver to steer a vehicle with less power, where the motor employs a Brushless Direct Current (BLDC) motor.
The BLDC motors have been increasingly used because the brushless motors are excellent in maintenance property, have a small size, and are capable of generating a high torque. The BLDC motor is a DC motor mounted with an electronic rectifying system, excluding those mechanical contact portions such as a brush and a rectifier from the conventional DC motor.
FIG. 1 is a lateral cross-sectional view of an EPS motor according to prior art. Referring to FIG. 1, the EPS motor includes a substantially cylindrical upper-opened housing (1), and a bracket (2) coupled to an upper surface of the housing (1) to form a general exterior look of the EPS motor.
The housing (1) and the bracket (2) are respectively supported by a rotation shaft (3). An upper surface of the rotation shaft (3) is connected to a steering shaft of a vehicle to provide a power to assist the steering of the vehicle. A periphery of the rotation shaft (3) is arranged with a rotor (5) formed with a core and a magnet. The housing (1) is connected at an inner circumferential surface to a stator (4) formed with a core and a coil to provide an electromagnetic force to the periphery of the rotor (5).
In a case a current is provided to the stator, the rotor (5) is rotated by electric interaction between the rotor and the stator to rotate the rotation shaft (3), thereby assisting rotation of the steering shaft.
The bracket (2) is formed thereon with a printed circuit board (PCB. 8) arranged with a sensor (9). The sensor (9) is discretely formed on an upper surface of the PCB (8) at a predetermined space to allow a plate (6) to rotate with the rotation shaft (3). A magnet (7) is formed at a lower side of the plate (6). The magnet (7) is rotated with the rotation of the rotation shaft (3) to calculate a rotational angle in response to magnetic flux generated by rotation detected by the sensor (9).
Thus, an appropriate current is provided to the stator in response to the rotational angle of the rotation shaft at the EPS motor to rotate the rotation shaft, whereby a steering torque can be assisted.
Meanwhile. FIG. 2 is a perspective view illustrating a separated state of a plate and a magnet according to prior art, and FIG. 3 is a perspective view illustrating the plate and the magnet that are coupled.
Generally, if the magnet (7) is magnetized to the plate (6), the plate (6) is coupled to the rotation shaft to a magnetic field direction to detect a position of the rotor (5). At this time, the plate (6) and the magnet (7) are coupled using an adhesive, such that it is difficult to accurately control the adhesive process and there is a probability of the magnet being disengaged from the plate (6).
Particularly, the coupling relationship between the plate and the magnet must be realized by a coupling force alone of the adhesive in view of the characteristics of a vehicle that is affected by various changing environments, which makes the coupling force of the adhesive more important.
The structure of using adhesive leads to a difficulty in choosing an adequate adhesive and an economic problem of using a high-priced adhesive. In addition, a problem arises of requiring an elaborate detailed work process in coating the adhesive.